Ligands for a Hairpin Precursor of a MicroRNA Linked to Cancer and Heart Disease We propose to identify, develop, and evaluate small peptidomimetic ligands for an RNA hairpin that is a precursor to a microRNA up-regulated in the development of heart disease and in many cancers. MicroRNAs are short, naturally occurring RNA molecules that regulate translation of messenger RNAs. Defined patterns of microRNA expression coincide with the translational dysregulation of a number of disease states. One microRNA, miR-21, is highly up- regulated in heart tissue that has diminished contractility due to prolonged stress. It is also highly up-regulated in a variety of tumors. Knockdown of this microRNA decreases the pathological phenotype in heart tissue and promotes programmed cell death in tumors, implicating it as a therapeutic target. MiR-21 is produced by excision from a longer primary transcript, where it is found in the stem of a hairpin structure. Endonucleases cleave the hairpin loop from the primary transcript and remove the apical loop. Thus, binding of a small molecule within or adjacent to this loop is a strategy for interfering with the processing of this microRNA and remedying the pathological consequences of its overproduction. Ligands for this RNA hairpin will be discovered by screening small molecule microarrays for lead compounds. The microarrays will comprise combinatorial libraries of linear and cyclic N-substituted oligo glycines (peptoids), which are drug-like in their cell permeability and protease resistance. After identifying lead compounds, their solution phase affinities and specificities for the targeted RNA will be tested, and the functional groups that contribute to affinity and specificity will be determined. This information will be used to create focused, second-generation libraries from which to derive compounds of improved affinity and specificity. Specificity will be assessed in vitro by measuring affinity to related RNA and by measuring the effect of competitor nucleic acids on the affinity for the target. Effects on maturation of miR-21 in cultured cells, specificity of these effects for miR-21 over other microRNAs, and effects on cell viability will be assessed for the most promising compounds. PUBLIC HEALTH RELEVANCE: The aim of the proposed research is to find compounds that bind to and diminish the function of RNA molecules involved in heart disease and cancer. The RNA molecules targeted are precursors to a recently discovered class called microRNAs. Thus, this research explores a potential new therapeutic strategy for the two diseases that are the leading causes of death in the United States.